Laminated thermostatic metal

ABSTRACT

A THREE LAYER LAMINATED METAL STRIP FOR USE IN CIRCUIT BREAKERS HAVING ADVANTAGES FLEXIVITY AND RESISTIVITY CHARACTERISTICS AND FORMED FROM A HIGH EXPANDING METAL LAMINATION, A LOW EXPANDING METAL LAMINATION AND AN ADDITIONAL LAMINATION DISPOSED BETWEEN THE LOW EXPANDING AND HIGH EXPANDING LAMINATIONS.

Feb. 16, 1971 c, zElGLER 3,563,712

LAMINATED THERMO-STATIC METAL Original Filed April 15, 1965 FJG. 4

INVENI OR CHARLES F. ZEIGLER BY M2 2 M ATTORNEYS United States Patent O3,563,712 LAMINATED THERMOSTATIC METAL Charles F. Zeigler, 4960Broomfield Lane, Birmingham, Mich. 48010 Continuation of applicationSer. No. 448,370, Apr. 15, 1965. This application May 2, 1968, Ser. No.726,113 Int. Cl. B23p 3/00 U.S. Cl. 29-195.5 1 Claim ABSTRACT OF THEDISCLOSURE CROSS REFERENCE TO RELATED APPLICATION This is a continuationof application S.N. 448,370, filed Apr. 15,, 1965, now abandoned.

SUMMARY OF THE INVENTION In accordance with the principles of myinvention, I provide a laminated metal strip having a first outer layerof high expanding metal such as 22% nickel, 3% chromium, balance iron; asecond outer layer of low expanding metal such as 42% nickel, balanceiron; and a third inner layer interposed between and bonded to bothouter layers, the third layer being formed from a metal of lowelectrical resistivity such as nickel. Typically, the outer layers areof substantially equal thickness and the inner layer is about twice asthick as either outer layer. The strip is formed with a dished centersection.

This strip finds its main present application in circuit breakers whichare maintained closed until the ambient temperature increases towardsame preselected maximum value at which the breaker is to snap open.This snap action is to be reversed when the temperature drops below thepreselected values.

My strip with the dished center section exhibits the desired propertiesfor this type of application, since it has low flexivity at temperaturesranging from perhaps 50 F. to about 300 F. and snaps over (highflexivity) at temperatures above 300 F. Moreover, my strip exhibits lowelectrical resistivity and will not respond to high current transients;without low resistivity, these transients would cause heating of thestrip itself and initiate snap action when the ambient temperatureremained below the selected value.

DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is an elevational view of a circuit breaker utilizing theimproved thermostatic metal of this invention, and showing the circuitbreaker contacts in engaged positions;

FIG. 2 is an elevational View of the circuit breaker of FIG. 1, showingthe thermostatic element of this invention in a deflected position so asto open the circuit breaker contacts;

FIG. 3 is a top View of the circuit breaker shown in FIG. 1; and

FIG. 4 is a diagrammatic sectional view of a thermostatic elementconstructed in accordance with the concepts of this invention.

3,563,712 Patented Feb. 16, 1971 DETAILED DESCRIPTION OF PREFERREDEMBODIMENTS Referring now to FIGS. 1 and 3 an element formed of thethermostatic metal of this invention, and indicated generally at 10, isdisposed in an illustrative circuit breaker 12 which itself forms nopart of the present invention and is illustrated only for the purpose ofillustrating the element 10 in an operative environment. The circuitbreaker 12 consists of a first conductor 16 having a fixed contact 18mounted on the terminal end thereof and a second conductor 20 which issecured to one end 22 of the thermostatic element 10, which end will behereinafter referred to as the fixed end 22. The opposite or movable end24 of the element 10 has a contact 26 secured thereto at a position suchthat the contacts 18 and 26 are engaged as shown at temperatures betweenroom temperature and a temperature of about 300 F. An insulating andspacer block 30 is secured to and positioned between conductors 16 and20 so as to maintain the conductors in a relatively insulated and spacedrelation. Element 10 is provided with a downwardly dished center section28.

The element 10 in the illustrated embodiment of the invention is ofgenerally rectangular shape, although it is to be understood that it canbe of other shapes, and in the illustrated circuit breaker 12 theelement 10 is cantilever mounted at its fixed end 22 on the conductor20.

One important feature of the element 10 is its inherent or intrinsicsnap action capability at the predetermined temperature of about 300 F.At this temperature, the element 10 will snap over to the position shownin FIG. 2 in which the contact is spaced from the contact 18. This snapaction is accomplished by forming the element 10 with a dished centersection 28, which is dished downwardly as referred to above.

The function of the element 10 is to maintain the movable contact 26 inengagement with the fixed contact 18 at temperatures below temperaturesof about 300 F. as shown in FIG. 1, and to move the contact 26 to aposition spaced from the contact 18 at a temperature above temperaturesabout 300 F., as shown in FIG. 2. It is intended that the element 10also maintain the contact 26 in engagement with the contact 18 duringflow of high overload currents of short duration (transients) throughthe conductors 16 and 20, when the temperature of element 10 is below300 F.

Referring now to FIG. 4, element 10' consists of two outer laminations34 and 36 and a center lamination 38. The outer lamination 34 is a lowexpanding metal lamination consisting of about 42% nickel with balanceiron. The lamination 36 is a high expanding metal lamination consistingof about 22% nickel, about 3% chromium with balance iron. The centerlamination is nickel. The lamination 34 is labeled lo in FIG. 4 and thelamination 36 is labeled hi to signify that the lamination 36 has ahigher coeflicient of thermal expansion than the lamination 34.

In order to obtain the desired flexivity and electrical resistivitycharacteristics in the element 10, the laminations must have relativeproportions at which laminations 34 and 36 are of approximately equalthicknesses and the combined thicknesses of the laminations 34 and 36must constitute about one half of the total thickness of the element 10.In a preferred embodiment of the invention, each of the laminations 34and 36 constitutes 26.7% of the total thickness and the lamination 38constitutes 46.6% of the thickness of the trimetal billet which issubsequently rolled out to provide an element 10 which is only a fewthousandths of an inch thick. Since, during roll out, one or more of thelaminations 34, 36 and 38 may be elongated more than the others, thefinal relative thicknesses of the laminations 34, 36 and 38 may varyslightly from the initial relative thicknesses.

The resulting trimetal has a flexivity in the range of temperaturesbetween 100 F. and 300 F. of 0.0000093 and an electrical resistivity at75 F. of 100 ohms per circular mil. ft. A resistivity on the order ofthis magnitude is required to preclude undesirable response of element10 to high electrical current transients, for if the element were torespond to these transients, the breaker would open when it shouldremain closed.

The element 10 has the desirable characteristics of sufficiently lowelectrical resistivity to prevent a response of the element 10 to highelectrical currents and a low flexivity at temperatures below 300 F. Ata temperature of about 300 F. or above, the element 10 has a higherflexivity so that, with the use of the dished center sectiou, it willquickly deflect and snap over. As shown in FIG. 4, the movable contact26 is secured to the high expanding lamination 36 at the movable end 24of the element 10. Lamination 36 is formed on the concave side of thesection 28. Consequently, when the element 10 responds to a hightemperature, it flexes in a direction to move the contact 26 away fromthe contact 18, as shown in FIG. 2.

From the above description it is seen that this invention provides animproved thermostatic metal which is operable, in an environment such asin a circuit breaker 12, to maintain the contacts 18 and 26 engaged whenthe temperature of the element 10 is below the critical temperature ofabout 300 F. Such construction also provides for lack of deflection ofelement 10 in response to high overload current conditions of shortduration.

It will be understood that the laminated thermostatic metal which ishereindisclosed and described is presented for purposes of explanationand illustration and is not intended to indicate limits of theinvention, the scope of which is defined by the following claim.

What is claimed is:

1. A thermostatic lamination adapted for use in a snap acting circuitbreaker comprising:

a central nickel layer;

a first high expanding outer layer parallel to the central layer andbonded metallurgically to one exposed surface of the central layer, saidfirst layer consisting essentially of 22% by weight of nickel, 3%chromium, balance iron;

a second low expanding outer layer parallel to the central layer andbonded metallurgically to the opposite exposed surface of the centrallayer, the second layer consisting essentially of 42% by weight ofnickel, balance iron; said first and second layers having equalthicknesses, the sum of the thicknesses of the first and second layersbeing equal to the thickness of the central layer; and a deformed regionextending transversely through all of the strips to define a circulardished center section which is concave as viewed from the exposedsurface of the first layer and is convex as viewed from the exposedsurface of the second layer.

References Cited UNITED STATES PATENTS 2,240,824 5/1941 Alban 29195.52,241,902 5/1941 Drapeau 29195.5 2,714,668 8/1955 Zinn 29195.5 2,481,0879/1949 Crise 29195.5 3,102,793 9/1963 Aban 29-195.5

HYLAND BIZOT, Primary Examiner

